Coal-fired boiler flue gas SO3 removal and low-temperature waste heat recovery system

Abstract

The utility model provides a coal-fired boiler flue gas SO3 removal and low-temperature waste heat recovery system, and belongs to the technical field of coal-fired boiler pollutant removal and waste heat recovery. Comprising a boiler body, an SCR denitration reactor, an air pre-heater, a dust remover, a booster fan, a desulfurization device and a chimney which are sequentially arranged in a communicating mode in the flue gas circulation direction, and further comprises an SO3 removal device, a first-stage low-temperature coal economizer and a second-stage low-temperature coal economizer, and the SO3 removal device communicates with the gas inlet end and the gas outlet end of the SCR denitration reactor; the first-stage low-temperature coal economizer is arranged between the air pre-heater and the dust remover, and the second-stage low-temperature coal economizer is arranged between the booster fan and the desulfurization device. According to the coal-fired boiler flue gas SO3 removal and low-temperature waste heat recovery system, coal-fired boiler flue gas SO3 removal and low-temperature waste heat recovery are organically combined, the problems of low-temperature corrosion and blockage of the heating surface at the tail of the boiler are effectively solved, and the reliability and stability of boiler operation are improved; low-temperature flue gas waste heat recovery is achieved, and boiler heat efficiency is improved.

Description

Technical Field

[0001] The present disclosure relates to the technical field of pollutant removal and waste heat recovery of coal-fired boilers, and particularly relates to a system for removing SO3 from the flue gas of a coal-fired boiler and recovering low-temperature waste heat. Background Art

[0002] At present, the exhaust gas loss of coal-fired boilers accounts for 60-80% of the total heat loss of the entire boiler. The increase in the exhaust gas temperature will directly cause a decrease in the boiler thermal efficiency. Research shows that for every 10°C increase in the exhaust gas temperature, the boiler thermal efficiency will decrease by 0.5-1%. In addition, the increase in the exhaust gas temperature will also bring problems such as a decrease in the efficiency of the tail-end electrostatic precipitator and an increase in the water consumption of wet flue gas desulfurization. Therefore, using a low-temperature economizer to recover the waste heat in the flue gas and reduce the exhaust gas temperature is considered an effective measure to improve the boiler thermal efficiency and the economy of the entire unit, and is an effective method to achieve pollution reduction and carbon emission reduction.

[0003] However, in coal-fired boilers, especially in high-sulfur coal-fired units, due to combustion and oxidation, some SO2 in the flue gas will be further oxidized to SO3, that is, the higher the SO2 concentration, the higher the SO3 concentration. And under ultra-low emissions, SCR technology is generally used for denitrification of coal-fired boilers. In addition to the denitrification function, the vanadium-tungsten-titanium catalyst for SCR denitrification can also catalytically oxidize SO2 to SO3, which further increases the SO3 concentration in the flue gas.

[0004] On the one hand, the SO3 concentration determines the acid dew point temperature of the flue gas. The higher the SO3 concentration, the higher the acid dew point temperature. If the surface temperature of the low-temperature heat exchange device at the tail of the boiler is lower than the acid dew point, the SO3 in the flue gas will condense and precipitate to form highly corrosive sulfuric acid, which will cause acid corrosion and lead to tube explosion, affecting the stable operation of the boiler. Therefore, the normal exhaust gas temperature of the boiler needs to be 15-20°C higher than the acid dew point. The higher the acid dew point of the flue gas, the higher the exhaust gas temperature, and the greater the exhaust gas heat loss.

[0005] On the other hand, SO3 is also prone to react with the ammonia and water escaping from SCR denitrification to form ammonium bisulfate. As the flue gas temperature decreases, ammonium bisulfate will condense into a highly viscous and corrosive liquid at about 150-280°C, and it is very easy to deposit on the surfaces of equipment such as air preheaters and the low-temperature economizer at the rear end, forming blockages and corrosion, making it difficult for the low-temperature heat exchange device at the tail of the boiler to operate normally for a long time, seriously affecting the thermal efficiency and stable operation of the coal-fired boiler.

[0006] The above problems are common in coal-fired boilers. Many coal-fired boilers can only be alleviated by raising the exhaust gas temperature and frequent shutdown for manual cleaning, resulting in low boiler thermal efficiency and insufficient operating rate. Utility Model Content

[0007] The object of the present disclosure is to overcome the deficiencies of the above-mentioned prior art, and to provide a system for removing SO3 from the flue gas of a coal-fired boiler and recovering low-temperature waste heat, so as to solve the problems of low-temperature corrosion and fouling blockage of the heating surface at the boiler tail, realize the recovery of low-temperature flue gas waste heat, and improve the boiler thermal efficiency.

[0008] To achieve the above-mentioned utility model object, the present disclosure adopts the following technical solutions:

[0009] A system for removing SO3 from the flue gas of a coal-fired boiler and recovering low-temperature waste heat, the system includes a boiler body, an SCR denitration reactor, an air preheater, a dust collector, a booster fan, a desulfurization device and a chimney which are connected in sequence along the flue gas flow direction, and further includes an SO3 removal device, a primary low-temperature economizer and a secondary low-temperature economizer. The SO3 removal device is respectively connected to the inlet end and the outlet end of the SCR denitration reactor. The primary low-temperature economizer is arranged between the air preheater and the dust collector, and the secondary low-temperature economizer is arranged between the booster fan and the desulfurization device.

[0010] In an exemplary embodiment of the present disclosure, the system further includes a blower and a warm air heater which are connected in sequence along the cold air flow direction. The outlet of the warm air heater is connected to the inlet of the air preheater, and the outlet of the air preheater is connected to the inlet of the boiler body.

[0011] In an exemplary embodiment of the present disclosure, the SO3 removal device includes:

[0012] An absorbent storage bin, which is arranged on one side of the SCR denitration reactor. The absorbent storage bin is sequentially connected with a feeding device and a mixer along the conveying direction of the absorbent;

[0013] Injection devices, which are respectively arranged at the inlet end and the outlet end of the SCR denitration reactor. The two injection devices are respectively connected to the outlet end of a distributor, and the inlet end of the distributor is connected to the outlet end of the mixer;

[0014] A conveying fan, which is arranged on the side of the mixer away from the distributor. The outlet of the conveying fan is connected to the inlet of the mixer.

[0015] In an exemplary embodiment of the present disclosure, the absorbent is a highly active calcium-based absorbent.

[0016] In an exemplary embodiment of the present disclosure, a feed water low-pressure heater is arranged on one side of the primary low-temperature economizer. The primary low-temperature economizer is connected to the feed water low-pressure heater, and the primary low-temperature economizer is used to heat the low-pressure feed water of the feed water low-pressure heater.

[0017] In an exemplary embodiment of the present disclosure, a waste heat recovery circulation pump is provided between the primary low-temperature economizer and the feed water low-pressure heater.

[0018] In an exemplary embodiment of the present disclosure, the secondary low-temperature economizer is connected to the air preheater, and the secondary low-temperature economizer is used to heat the feed water of the air preheater.

[0019] In an exemplary embodiment of the present disclosure, a circulating water pump for the air preheater is provided between the secondary low-temperature economizer and the air preheater.

[0020] In an exemplary embodiment of the present disclosure, the temperature of the flue gas after passing through the primary low-temperature economizer is 100 - 110 degrees Celsius.

[0021] In an exemplary embodiment of the present disclosure, the temperature of the flue gas after passing through the secondary low-temperature economizer is 80 - 90 degrees Celsius.

[0022] Advantages of the present utility model:

[0023] (1) In the present utility model, a SO3 removal device is provided in the coal-fired boiler, and absorbent injection devices are respectively provided before and after the SCR denitration reactor, which prolongs the reaction time of the absorbent and the flue gas. Through two-stage combined removal, efficient removal of SO3 in the flue gas is achieved, and the acid dew point temperature of the flue gas is reduced.

[0024] (2) In the present utility model, the SO3 removal absorbent uses a calcium-based absorbent with a large specific surface area and high activity, which reduces the influence of the absorbent on the catalyst activity, has a high SO3 removal efficiency, less absorbent consumption, and a higher cost performance of the calcium-based absorbent.

[0025] (3) On the basis of the SO3 removal device, the present utility model adds a low-temperature economizer for deep waste heat utilization. Compared with the conventional flue gas discharge temperature of 130 °C, the flue gas discharge temperature of the present utility model can be reduced by 40 - 50 °C, and the flue gas discharge temperature is reduced to 80 - 90 °C, greatly reducing the flue gas discharge loss of the boiler and improving the boiler efficiency.

[0026] (4) In the present utility model, two-stage low-temperature economizers are provided. The high-temperature primary low-temperature economizer is used to heat the feed water low-pressure heater, reducing the steam consumption of the low-pressure heater and increasing the power generation of the steam turbine; the low-temperature secondary low-temperature economizer is used to heat the primary (secondary) air at the inlet of the air preheater, increasing the inlet air temperature of the air preheater and avoiding low-temperature corrosion.

[0027] (5) In the present utility model, the removal of SO3 from the flue gas of a coal-fired boiler is organically combined with low-temperature waste heat recovery, effectively solving the problems of low-temperature corrosion and fouling blockage of the heating surfaces at the boiler tail, enabling reliable and stable operation of low-temperature heating surfaces such as the air preheater and low-temperature economizer of the boiler, improving the reliability and stability of boiler operation, efficiently realizing low-temperature flue gas waste heat recovery, increasing the boiler thermal efficiency, and achieving comprehensive reduction of pollution and carbon emissions in the flue gas. Description of the Drawings

[0028] The drawings herein are incorporated into and constitute a part of this specification, showing embodiments in accordance with the present disclosure, and are used together with the specification to explain the principles of the present disclosure. Obviously, the drawings in the following description are only some embodiments of the present disclosure, and those of ordinary skill in the art can obtain other drawings based on these drawings without creative efforts.

[0029] Figure 1 In one embodiment of the present disclosure, it is a schematic structural diagram of a system for removing SO3 from the flue gas of a coal-fired boiler and recovering low-temperature waste heat.

[0030] Description of the Reference Numerals in the Drawings:

[0031] 1. Boiler body; 2. SCR denitration reactor; 3. Air preheater; 4. Blower; 5. Air heater; 6. First-stage low-temperature economizer; 7. Dust collector; 8. Booster fan; 9. Second-stage low-temperature economizer; 10. Desulfurization device; 11. Chimney; 12. Absorbent storage bin; 13. Feeding device; 14. Mixer; 15. Delivery fan; 16. Distributor; 17. Injection device; 18. Feed water low-pressure heater; 19. Waste heat recovery circulation pump; 20. Air heater circulation water pump. Detailed Embodiments

[0032] Example embodiments will now be described more fully with reference to the drawings. However, the example embodiments can be implemented in various forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of the example embodiments to those skilled in the art. Like reference numerals in the drawings denote the same or similar structures, and thus their detailed descriptions will be omitted. In addition, the drawings are only schematic illustrations of the present disclosure and are not necessarily drawn to scale.

[0033] Although relative terms such as "upper" and "lower" are used in this specification to describe the relative relationship of one component of an icon to another component, these terms are used in this specification only for convenience, for example, according to the directions of the examples described in the drawings. It can be understood that if the device of the icon is flipped so that it is upside down, the component described as "upper" will become the component "lower". When a structure is "on" another structure, it may mean that a structure is integrally formed on another structure, or that a structure is "directly" disposed on another structure, or that a structure is "indirectly" disposed on another structure through another structure.

[0034] The terms "a", "an", "the", "said" and "at least one" are used to indicate the presence of one or more elements / components / etc.; the terms "comprising" and "having" are used to mean an open inclusion and mean that there may be additional elements / components / etc. in addition to the listed elements / components / etc.; the terms "first", "second", "third", etc. are used only as labels and are not a limitation on the quantity of their objects.

[0035] The embodiments of the present disclosure provide a system for removing SO3 from flue gas of a coal-fired boiler and recovering low-temperature waste heat. Refer to Figure 1 , the system includes a boiler body 1, an SCR denitration reactor 2, an air preheater 3, a dust collector 7, a booster fan 8, a desulfurization device 10, and a chimney 11 that are connected in sequence along the flue gas flow direction, and further includes an SO3 removal device, a primary low-temperature economizer 6, and a secondary low-temperature economizer 9. The SO3 removal device is respectively connected to the inlet end and the outlet end of the SCR denitration reactor 2. The primary low-temperature economizer 6 is arranged between the air preheater 3 and the dust collector 7, and the secondary low-temperature economizer 9 is arranged between the booster fan 8 and the desulfurization device 10.

[0036] In the embodiments of the present disclosure, the system for removing SO3 from flue gas of a coal-fired boiler and recovering low-temperature waste heat is composed of a boiler body 1, an SCR denitration reactor 2, an air preheater 3, a dust collector 7, a booster fan 8, a desulfurization device 10, a chimney 11, an SO3 removal device, a primary low-temperature economizer 6, and a secondary low-temperature economizer 9 that are connected in sequence along the flue gas flow direction. The SO3 removal device is arranged on one side of the SCR denitration reactor 2, and the SO3 removal device is connected to the inlet end and the outlet end of the SCR denitration reactor 2. When the flue gas enters the SCR denitration reactor 2, the SO3 in the original flue gas is removed through the SO3 removal device; the primary low-temperature economizer 6 is installed between the air preheater 3 and the dust collector 7, and the secondary low-temperature economizer 9 is installed between the booster fan 8 and the desulfurization device 10. The low-temperature waste heat of the flue gas is recovered through the segmented primary low-temperature economizer 6 and secondary low-temperature economizer 9.

[0037] In the embodiment of the present disclosure, the high-temperature flue gas generated by the boiler body 1 first passes through the SCR denitration reactor 2 for denitration. A denitration vanadium-titanium catalyst is provided in the SCR denitration reactor 2. NOx in the flue gas reacts with the injected reducing agent ammonia under the action of the catalyst to remove nitrogen oxides. However, a part of SO2 in the flue gas is oxidized to SO3 under the action of the catalyst. SO3 easily reacts with the escaped denitration ammonia water to generate ammonium bisulfate, causing blockage and corrosion of the air preheater 3. Therefore, in order to remove SO3 in the flue gas, an SO3 removal device is arranged before and after the SCR denitration reactor 2. The flue gas after SO3 removal passes through the air preheater 3, enters the primary low-temperature economizer 6 to reduce the flue gas discharge temperature, and then passes through the dust collector 7 and the booster fan 8 to transport the flue gas to the secondary low-temperature economizer 9 to further reduce the flue gas discharge temperature. Finally, it is discharged into the atmosphere from the chimney 11 after passing through the desulfurization device 10.

[0038] Compared with the existing flue gas SO3 removal and low-temperature waste heat recovery devices, the flue gas SO3 removal and low-temperature waste heat recovery system of this coal-fired boiler organically combines the removal of flue gas SO3 and low-temperature waste heat recovery, effectively solves the problems of low-temperature corrosion and blockage of the heating surfaces at the boiler tail, enables the reliable and stable operation of low-temperature heating surfaces such as the boiler air preheater and low-temperature economizer, improves the reliability and stability of boiler operation, efficiently realizes the recovery of low-temperature flue gas waste heat, improves the boiler thermal efficiency, and realizes comprehensive reduction of flue gas pollution and carbon emissions.

[0039] In one embodiment of the present disclosure, referring to Figure 1 , the system further includes a blower 4 and a air heater 5 connected in sequence along the cold air flow direction. The air outlet of the air heater 5 is connected to the air inlet of the air preheater 3, and the air outlet of the air preheater 3 is connected to the air inlet of the boiler body 1. In this way, the fresh air entering the air preheater 3 and the boiler body 1 can be preheated, the temperature of the fresh air can be increased, and the corrosion risk of the air preheater 3 can be reduced.

[0040] In one embodiment of the present disclosure, referring to Figure 1 , the SO3 removal device includes: an absorbent storage bin 12, arranged on one side of the SCR denitration reactor 2. The absorbent storage bin 12 is sequentially connected with a feeding device 13 and a mixer 14 along the conveying direction of the absorbent; injection devices 17, respectively arranged at the inlet end and the outlet end of the SCR denitration reactor 2. The two injection devices 17 are respectively connected to the outlet end of a distributor 16, and the inlet end of the distributor 16 is connected to the outlet end of the mixer 14; a conveying fan 15, arranged on the side of the mixer 14 away from the distributor 16. The air outlet of the conveying fan 15 is connected to the air inlet of the mixer 14. In this way, the efficient removal of SO3 in the flue gas can be realized, and the acid dew point temperature of the flue gas can be reduced.

[0041] It can be understood that the absorbent stored in the absorbent storage bin 12 is transported to the injection device 17 before and after the SCR denitrification reactor 2 through the feeding device 13 and the mixer 14, with the power source provided by the conveying fan 15. Under the action of the distributor 16, the absorbent is transported to the injection device 17 before and after the SCR denitrification reactor 2. The injection device 17 injects the absorbent into the flue to react with the flue gas, completes the removal of SO3, reduces the acid dew point temperature of the flue gas, and creates favorable conditions for the recovery of low-temperature waste heat at the tail of the boiler.

[0042] Optionally, the absorbent is a highly active calcium-based absorbent. In this way, the absorbent has a large specific surface area and high activity, which can reduce the influence of the absorbent on the activity of the catalyst and improve the removal efficiency of SO3.

[0043] In one example, a high-efficiency calcium-based absorbent is sprayed at the inlet of the SCR denitrification reactor 2 through an injection device 17 to remove SO3 from the original flue gas, thereby preventing SO3 from reacting with ammonia sprayed in the SCR denitrification reactor 2 to form ammonium bisulfate. At the same time, the reaction time between the absorbent and the flue gas is increased through the SCR denitrification reactor 2, thereby improving the SO3 removal effect.

[0044] In one example, a high-efficiency calcium-based absorbent is sprayed at the outlet of the SCR denitrification reactor 2 through an injection device 17 as a supplement to the inlet of the SCR denitrification reactor 2, and is used to remove SO3 generated by the denitrification reaction in the SCR denitrification reactor 2, and reduce the reaction of SO3 with escaped ammonia to generate ammonium bisulfate.

[0045] Obviously, the SO3 removal device is provided with injection devices 17 at the inlet and outlet of the SCR denitrification reactor 2, respectively. Through the two-stage combined removal, the efficient removal of SO3 is effectively ensured, so that the generation of ammonium bisulfate is greatly reduced, thereby making the air preheater 3, the first-stage low-temperature economizer 6, the dust collector 7, and the second-stage low-temperature economizer 9 operate efficiently and stably without blockage and corrosion problems.

[0046] Optionally, the calcium-based absorbent is transported to the absorbent storage bin 12 by an external tanker.

[0047] In one embodiment of the present disclosure, see Figure 1 A feedwater low-pressure heater 18 is provided on one side of the primary low-temperature economizer 6, and the primary low-temperature economizer 6 is connected to the feedwater low-pressure heater 18. The primary low-temperature economizer 6 is used to heat the low-pressure feedwater of the feedwater low-pressure heater 18; a waste heat recovery circulation pump 19 is provided between the primary low-temperature economizer 6 and the feedwater low-pressure heater 18. In this way, the flue gas heat can be used to heat the low-pressure feedwater, realizing the primary waste heat recovery of the flue gas.

[0048] In one example, a water supply pipe is spirally arranged in the primary low-temperature economizer 6. One end of the water supply pipe is communicated with the water inlet end of the feed water low-pressure heater 18, and the other end of the water supply pipe is communicated with the water outlet end of the feed water low-pressure heater 18. The waste heat recovery circulation pump 19 is arranged between the water inlet end of the feed water low-pressure heater 18 and the water supply pipe.

[0049] In another example, a water supply pipe is spirally wound around the surface of the primary low-temperature economizer 6. One end of the water supply pipe is communicated with the water inlet end of the feed water low-pressure heater 18, and the other end of the water supply pipe is communicated with the water outlet end of the feed water low-pressure heater 18. The waste heat recovery circulation pump 19 is arranged between the water inlet end of the feed water low-pressure heater 18 and the water supply pipe.

[0050] It can be understood that the heat of the flue gas in the primary low-temperature economizer 6 is transferred to the feed water low-pressure heater 18 through the spirally arranged water supply pipe, and the feed water power is provided by the waste heat recovery circulation pump 19, so that the low-pressure feed water continuously flows in the water supply pipe, realizing continuous heating of the low-pressure feed water, reducing the steam consumption of the feed water low-pressure heater 18, increasing the power generation, and further realizing the reduction of the flue gas temperature, the increase of the dust resistivity, and the improvement of the efficiency of the dust collector 7.

[0051] In an embodiment of the present disclosure, refer to Figure 1 , the secondary low-temperature economizer 9 is connected to the air heater 5, and the secondary low-temperature economizer 9 is used to heat the feed water of the air heater 5; a circulating water pump 20 for the air heater is arranged between the secondary low-temperature economizer 9 and the air heater 5. In this way, the heat of the flue gas can be used to heat the primary (secondary) air, realizing the secondary waste heat recovery of the flue gas.

[0052] In one example, a first water supply pipe is spirally arranged in the secondary low-temperature economizer 9, and a second water supply pipe is spirally arranged in the air heater 5. The water outlet of the first water supply pipe is communicated with the water inlet of the second water supply pipe, and the water inlet of the first water supply pipe is communicated with the water outlet of the second water supply pipe. The circulating water pump 20 for the air heater is arranged between the water outlet of the first water supply pipe and the water inlet of the second water supply pipe.

[0053] In another example, a first water supply pipe is spirally wound around the surface of the secondary low-temperature economizer 9, and a second water supply pipe is spirally wound around the surface of the air heater 5. The water outlet of the first water supply pipe is communicated with the water inlet of the second water supply pipe, and the water inlet of the first water supply pipe is communicated with the water outlet of the second water supply pipe. The circulating water pump 20 for the air heater is arranged between the water outlet of the first water supply pipe and the water inlet of the second water supply pipe.

[0054] It can be understood that through the first water supply pipe and the second water supply pipe arranged in a spiral manner, the heat of the flue gas in the secondary low-temperature economizer 9 is transferred to the air preheater 5. The water supply power is provided by the air preheater circulating water pump 20, so that the water continuously flows in the water supply pipe, realizing the circulating heat exchange of the water flow in the water supply pipe, heating the primary (secondary) air at the outlet of the blower 4 through the air preheater 5, increasing the air temperature on the side of the air preheater 3, reducing the corrosion risk of the air preheater 3. At the same time, the increase in the temperature of the primary and secondary air helps the boiler to burn stably and efficiently.

[0055] In an embodiment of the present disclosure, the temperature of the flue gas after passing through the primary low-temperature economizer 6 is 100-110 degrees. In this way, the temperature of the flue gas can be reduced once, and the waste heat of the flue gas can be recovered and utilized once.

[0056] In an embodiment of the present disclosure, the temperature of the flue gas after passing through the secondary low-temperature economizer 9 is 80-90 degrees. In this way, the temperature of the flue gas can be reduced twice, and the waste heat of the flue gas can be recovered and utilized twice.

[0057] According to the above two embodiments, after the flue gas is heat-exchanged by the air preheater 3, the temperature of the flue gas is 130-140 °C. After the flue gas passes through the primary low-temperature economizer 6 for cooling, the temperature is 100-110 °C. After the flue gas passes through the secondary low-temperature economizer 9 for cooling, the temperature is 80-90 °C. Compared with the conventional flue gas discharge temperature of 130 °C, the flue gas temperature is reduced by 40-50 °C, realizing the deep waste heat utilization of the flue gas, greatly reducing the flue gas discharge loss of the boiler, improving the thermal efficiency of the boiler, and realizing the comprehensive reduction of pollution and carbon emissions of the flue gas.

[0058] After considering the specification and practicing the utility model disclosed herein, those skilled in the art will readily think of other embodiments of the present disclosure. This application is intended to cover any variations, uses, or adaptations of the present disclosure, which follow the general principles of the present disclosure and include the common general knowledge or conventional technical means in the technical field not disclosed in the present disclosure. The specification and examples are only regarded as exemplary, and the true scope and spirit of the present disclosure are pointed out by the appended claims.

Claims

1. A system for removing SO3 from flue gas of a coal-fired boiler and recovering low-temperature waste heat, the system comprising a boiler body (1), an SCR denitration reactor (2), an air preheater (3), a dust collector (7), a booster fan (8), a desulfurization device (10) and a chimney (11) which are sequentially connected and arranged along the flue gas flow direction, characterized in that: It also includes a SO3 removal device, a first-level low-temperature economizer (6) and a second-level low-temperature economizer (9), wherein the SO3 removal device is respectively connected to the air inlet and the air outlet of the SCR denitration reactor (2), the first-level low-temperature economizer (6) is arranged between the air preheater (3) and the dust collector (7), and the second-level low-temperature economizer (9) is arranged between the booster fan (8) and the desulfurization device (10).

2. A coal-fired boiler flue gas SO3 removal and low-temperature waste heat recovery system according to claim 1, characterized in that: The system further comprises a blower (4) and an air heater (5) which are connected in sequence along the cold air circulation direction; the air outlet of the air heater (5) is connected to the air inlet of the air preheater (3); and the air outlet of the air preheater (3) is connected to the air inlet of the boiler body (1).

3. A coal-fired boiler flue gas SO3 removal and low-temperature waste heat recovery system according to claim 1, characterized in that: The SO3 removal device comprises: An absorbent storage bin (12) is disposed on one side of the SCR denitration reactor (2), and the absorbent storage bin (12) is sequentially connected to a feeding device (13) and a mixer (14) along a conveying direction of the absorbent; The injection devices (17) are respectively arranged at the air inlet end and the air outlet end of the SCR denitration reactor (2), the two injection devices (17) are respectively connected to the discharge end of the distributor (16), and the feed end of the distributor (16) is connected to the discharge end of the mixer (14); A conveying fan (15) is arranged on a side of the mixer (14) away from the distributor (16), and an air outlet of the conveying fan (15) is connected to an air inlet of the mixer (14).

4. A coal-fired boiler flue gas SO3 removal and low-temperature waste heat recovery system according to claim 3, characterized in that: The absorbent is a highly active calcium-based absorbent.

5. A coal-fired boiler flue gas SO3 removal and low-temperature waste heat recovery system according to claim 1, characterized in that: A feed water low-pressure heater (18) is provided on one side of the first-stage low-temperature economizer (6). The first-stage low-temperature economizer (6) is connected to the feed water low-pressure heater (18). The first-stage low-temperature economizer (6) is used to heat the low-pressure feed water of the feed water low-pressure heater (18).

6. A coal-fired boiler flue gas SO3 removal and low-temperature waste heat recovery system according to claim 5, characterized in that: A waste heat recovery circulation pump (19) is provided between the first-stage low-temperature economizer (6) and the feed water low-pressure heater (18).

7. A coal-fired boiler flue gas SO3 removal and low-temperature waste heat recovery system according to claim 2, characterized in that: The secondary low-temperature economizer (9) is connected to the air heater (5), and the secondary low-temperature economizer (9) is used to heat the feed water of the air heater (5).

8. A coal-fired boiler flue gas SO3 removal and low-temperature waste heat recovery system according to claim 7, characterized in that: A heater circulating water pump (20) is provided between the secondary low-temperature economizer (9) and the heater (5).

9. A coal-fired boiler flue gas SO3 removal and low-temperature waste heat recovery system according to claim 1, characterized in that: The temperature of the flue gas after passing through the first-stage low-temperature economizer (6) is 100-110 degrees.

10. A coal-fired boiler flue gas SO3 removal and low-temperature waste heat recovery system according to claim 1, characterized in that: The temperature of the flue gas after passing through the secondary low-temperature economizer (9) is 80 to 90 degrees.

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